We believe it is because of the wrong usage stats migration/upgrade scripts, but unfortunately we still haven’t found the right solution As soon as we find an answer, I will post it here…
Would it be maybe possible for you to test this upgrade patch, if that works for your installation: metrics migration · bozana/ojs@55e8440 · GitHub ? I.e. you would need to apply the patch on the OJS 3.0 code and run php tools/upgrade.php upgrade again. Please do not forget to first backup everything! If it works, could you also take a look at your DB table metrics and if everything looks fine there, i.e. if your OJS views and/or TimedViews are there… And finally, if it works please wait just a little bit more, till we tested it with a few other installations as well and merged in into the code, before you apply it for real.